Copolymerizable photoinitiators for UV-crosslinkable adhesives

ABSTRACT

The invention relates to radically copolymerizable acetophenone or benzophenone derivatives, obtained by reaction of
     a) (meth)acrylic compounds exhibiting at least one isocyanate-reactive group [compounds a)] with   b) compounds exhibiting at least two isocyanate groups [compounds b)] and   c) acetophenone or benzophenone derivatives exhibiting at least one isocyanate-reactive group [compounds c)].   

     The invention also relates to copolymers that contain copolymerizable photoinitiators of the invention and to the use of said copolymers in UV-crosslinkable compositions, particularly hot-melt adhesives.

The invention relates to radically copolymerizable acetophenone orbenzophenone derivatives (referred to below as “copolymerizablephotoinitiators” for the sake of brevity), obtained by the reaction of

-   a) (meth)acrylic compounds, having at least one isocyanate-reactive    group [compounds a)] with-   b) compounds having at least two isocyanate groups [compounds b)]    and-   c) acetophenone or benzophenone derivatives having at least one    isocyanate-reactive group [compounds c)].

The invention also relates to copolymers which contain thecopolymerizable photoinitiators of the invention and to the use of thecopolymers in UV-crosslinkable compositions, for example, as adhesives,particularly hot-melt adhesives.

UV-crosslinkable adhesives containing photoinitiators in the form ofpolymerized units, are disclosed, for example, in specifications DE-A2,411,169 and EP-A 246,848.

Copolymerizable benzophenone or acetophenone derivatives are described,for example, in specifications EP-A 346,788 and EP-A 377,199.

Copolymerizable photoinitiators should be producible in a simple mannerand be readily copolymerizable, and the copolymers containingphotoinitiators should exhibit, in use, good application-technologicalproperties, particularly high cohesion and adhesion when used asadhesives.

It is an object of the present invention to provide novelcopolymerizable photoinitiators, and copolymers containing thephoto-initiators of the invention in the form of polymerized units andexhibiting, when used as adhesives, improved cohesion and adhesion.

Accordingly, we have found the copolymerizable photoinitiators definedabove, copolymers containing the same, and the use thereof inUV-crosslinkable compositions.

The compounds a) are, for example, (meth)acrylic compounds of thegeneral formula (I)H₂C═CR²—C(═O)—X—R²(—Y)_(π)  (I),in which the substituents and indices have the following meanings:

-   R¹ denotes —H, —CH₃,-   X denotes —O—, —NH—, —NR³— or —S—, preferably —O—,-   R³ denotes linear or branched C₁-C₆ alkyl,-   R² denotes a (n+1)-binding,    -   optionally substituted linear or branched C₁-C₁₂ alkyl group,        preferably a C₂-C₈ alkyl group, or    -   a C₃-C₁₂ cycloalkyl group, optionally substituted, preferably a        C₅ and C₆ cycloalkyl group, or    -   a C₆-C₁₀ aryl group, optionally substituted, preferably a phenyl        group,-   Y denotes —OH, —NH₂, —NHR³ or —SH, preferably —OH,-   π is a number from 1 to 5, preferably 1.

In formula (I) the structural element —R²(—Y)_(π) can alternatively be agroup of the general formula (II), (III) or (IV)-(EO)_(k)—(PO)_(l)—H  (II),—(PO)_(l)-(EO)_(k)—H  (III),-(EO_(k)/PO_(l))—H  (IV),in which

-   EO stands for a —CH₂—CH₂—O group,-   PO stands for a —CH₂—CH(CH₃)—O or a —CH(CH₃)—CH₂—O group and k and 1    for numerical values from 0 to 15, frequently from 0 to 10 and often    from 0 to 5, but k and 1 are not both 0. Frequently either k or 1 is    equal to 1, 2, 3, or 4 and often to 1.

Furthermore, in formulas (II) and (III)

-   -   (EO)_(k) should denote a block of k —CH₂—CH₂—O groups, and        (PO)_(l) a block of l —CH₂—CH(CH₃)—O or —CH(CH₃)—CH₂—O groups,        and        in formula (IV) (EO_(k)/PO_(l)) should denote a mixture of k        —CH₂—CH₂—O groups and l —CH₂—CH(CH₃)—O or —CH(CH₃)—CH₂—O groups        in random distribution.

A significant fact is that in formulas (II), (III), or (IV) either EQ orPO can be replaced by BO, where BO stands for a —CH₂—CH(C₂H₅)—O or a—CH(C₂H₅)—CH₂—O group as well as a —CH₂—C(CH₃)₂—O or a —C(CH₃)₂—CH₂—Ogroup.

By linear or branched C₁-C₆ alkyl is meant linear or branched alkylcontaining from 1 to 6 carbons, for example, methyl, ethyl, n-propyl,isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl,isopentyl, tert-pentyl, n-hexyl, isohexyl, or tert-hexyl.

By a (π+1)-binding, linear or branched C₁-C₁₂ alkyl group we mean alkylderived from, for example, methyl, ethyl, propyl, 2-methylpropyl,2,2-dimethylpropyl, and n-butyl and isomers thereof, n-pentyl andisomers thereof, n-hexyl and isomers thereof, n-heptyl and isomersthereof, n-octyl and isomers thereof, n-nonyl and isomers thereof,n-decyl and isomers thereof, n-undecyl and isomers thereof, or n-dodecyland isomers thereof. Of course, the aforementioned alkyl groups may besubstituted by further mono-, di-, or tri-functional groups, such ashalogens, ie fluorine, chlorine, or bromine, or alkoxyl groups, such asmethoxy, ethoxy, or butoxy groups, in which case the covalence of thealkyl groups rises by the number of such substituents.

By (π+1)-binding C₃-C₁₂ cycloalkyl groups we mean (π+1)-bindingcycloalkyl groups derived, for example, from cyclopropyl, cyclobutyl,cyclopentyl, cyclohexyl, cycloheptyl cyclooctyl, cyclononyl, orcyclodecyl. Furthermore they may be taken to mean bicyclic compoundsderived from bicyclohexane, bicycloheptane, bicyclooctane,bicyclononane, bicyclodecane, and bicycloundecane or bicyclododecane. Ofcourse, the aforementioned cycloalkyl groups may be substituted byfurther mono-, di-, or tri-functional groups, such as C₁-C₆ alkylgroups, halogens, or alkoxyl groups, in which case the covalence of thecycloalkyl rises by the number of such substituents. Frequently1,2-cyclopropylene, [1,2 or 1,3]-cyclobutylene, [1,2 or1,3]-cyclopentylene, [1,2, 1,3, or 1,4]-cyclohexylene, [1,2, 1,3, or1,4]-cycloheptylene, bicyclooctylene, bicyclononylene, bicyclodecyleneand bicycloundecylene groups are used.

By (π+1)-binding C₆-C₁₀ aryl groups we mean (π+1)-binding aryl groupsderived from phenyl or naphthyl groups. Of course, the aforementionedaryl groups may be substituted by 1, 2, or 3 substituents, such as C₁-C₆alkyl groups, halogens, or alkoxyl groups, in which case the covalenceof the aryl groups rises by the number of these substituents.Frequently, use is made, in particular, of [1,3 and 1,4]-phenylene or[1,3, 1,4, 1,5, and 2,6]-naphthylene groups.

An essential feature is that the aforementioned groups R² aresubstituted by π Y groups. π denotes here a number from 1 to 5, forexample, 1, 2, 3, 4 or 5, but particularly 1.

Compounds a) used are, in particular: 2-hydroxyethyl(meth)acrylate,2-hydroxy-2-methylethyl(meth)acrylate, 3-hydroxypropyl (meth)acrylate,2-hydroxy-2-ethylethyl(meth)acrylate, 4-hydroxybutyl (meth)acrylate,further neopentyl glycol mono(meth)acrylate, glycerolmono(meth)acrylate, trimethylolpropane mono(meth)acrylate,pentaerythritol mono(meth)acrylate, N-hydroxyymethyl(meth)acrylamide,and N-hydroxyethyl(meth)acrylamide,5-hydroxy-3-oxopentyl(meth)acrylamide, N-hydroxymethylcrotonamide orN-hydroxyethylmaleinimide. Particular preference is given to2-hydroxyethyl(meth)acrylate, 3-hydroxypropyl acrylate, and4-hydroxybutyl(meth)acrylate.

Compounds b) containing at least 2 isocyanate groups usually exhibit thestructure of the general formula (V)Q(-NCO)_(λ)  (V).

In formula (V), Q should denote, for example,

-   -   a linear or branched C₃-C₁₆ alkane compound, for example,        propane, 2-methylpropane, 2,2-dimethylpropane, n-butane and        isomers thereof, n-pentane and isomers thereof, n-hexane and        isomers thereof, n-heptane and isomers thereof, n-octane and        isomers thereof, n-nonane and isomers thereof, n-decane and        isomers thereof, n-undecane and isomers thereof, and n-dodecane        and isomers thereof, n-tridecane and isomers thereof,        n-tetradecane and isomers thereof, n-pentadecane and isomers        thereof and also n-hexadecane and isomers thereof, preferably a        C₆-C₁₃ alkane compound, optionally substituted by 1, 2 or 3        halogens, oxo, ester, or alkoxy groups, or    -   a C₆-C₁₄ aromatic compound, for example, benzene,        diphenylmethane, naphthalene, phenanthrene, preferably benzene        and diphenylmethane, optionally substituted by 1, 2, or 3        halogens, C₁-C₆ alkyl, oxo, ester, or alkoxy groups, or    -   a C₃-C₁₆ cycloalkane compound, for example, cyclopropane,        cyclobutane, cyclopentane, cyclohexane, cycloheptane,        cyclooctane, bicyclooctane, bicyclononane, bicyclodecane,        bicycloundecane, bicyclododecane, and bis(cyclohexyl)methane,        preferably cyclopentane, cyclohexane, bis(cyclohexyl)methane,        optionally substituted by 1, 2, or 3 halogens, C₁-C₆ alkyl, oxo,        ester, or alkoxy groups, or    -   an arylalkyl compound containing from 6 to 10 carbons in the        aryl moiety and from 1 to 6, preferably from 1 to 4 carbon atoms        in the alkyl moiety, optionally further substituted by 1, 2, or        3 halogens, oxo, ester, or alkoxy groups,        which is substituted by λ isocyanate groups (—NCO), λ, which        denotes the average functionality, being a number ≧2, often a        number from 2 to 6, and frequently a number from 2 to 4. In        particular, λ is equal to 2.

Examples of compounds of the general structure (V) are aliphatic,cycloaliphatic, and aromatic isocyanates known from the prior art.Preferred di- or poly-isocyanates are 4,4′-diphenylmethane diisocyanate,the mixtures of monomeric diphenylmethane diisocyanates and oligomericdiphenylmethane diisocyanates (polymeric MDI), tetramethylenediisocyanate, tetramethylene diisocyanate trimers, hexamethylenediisocyanate, hexamethylene diisocyanate trimers, isophoronediisocyanate trimer, 4,4′-methylenebis(cyclohexyl) diisocyanate,xylylene diisocyanate, tetramethylxylylene diisocyanate, [1,3 and1,4]-bis(isocyanatomethyl)cyclohexanes, dodecyl diisocyanate, lysinealkylester diisocyanate, alkyl standing for C₁ to C₁₀, [2,2,4 or2,4,4]-trimethyl-1,6-hexamethylene diisocyanate,1,4-diisocyanatocycohexane or 4-isocyanatomethyl-1,8-octamethylenediisocyanate.

Special preference is given to di- or poly-isocyanates containingisocyanate groups of different reactivity, such as 2,4-toluoylenediisocyanate (2,4-TDI), 2,4′-diphenylmethane diisocyanate (2,4′-MDI),triisocyanatotoluene, isophorone diisocyanate (IPDI)2-butyl-2-ethylpentamethylene diisocyanate, and2-isocyanatopropylcyclohexyl isocyanate, 3(4)isocyanatomethyl-1-methylcyclohexyl isocyanate,1,4-diisocyanato-4-methylpentane, 2,4′-methylenebis(cyclohexyl)diisocyanate and 4-methylcyclohexane 1,3-diisocyanate (H-TDI).

Furthermore, those isocyanates are particularly preferred whoseisocyanate groups are originally equally reactive, but in which initialaddition of an alcohol, thiol, or amine to one of the isocyanate groupscan induce a reduction of the reactivity of the second isocyanate group.Examples thereof are isocyanates whose isocyanate groups are coupledthrough a delocalized electron system, eg, [1,3 and 1,4]-phenylenediisocyanate, 1,5-naphthylene diisocyanate, diphenyl diisocyanate,tolidine diisocyanate, or 2,6-toluoylene diisocyanate.

Another significant fact is that suitable compounds of the generalformula (V) are also those di- and poly-isocyanate compounds which canbe produced from said di- or poly-isocyanates or mixtures thereof bylinking through urethane, allophanate, urea, biuret, uretdione, amide,isocyanurate, carbodiimide, uretoneimine, oxadiazinetrione, oriminooxadiazinedione structures.

Compounds c) used in the present invention exhibit, for example, astructure conforming to general formula (VI)A-C(═O)—B-D  (VI),in which

-   A denotes C₁-C₃ alkyl, such as methyl, ethyl, n-propyl, or    isopropyl, C₆-C₁₀ aryl, optionally substituted by 1, 2 or 3    halogens, C₁-C₆ alkyl, esters or alkoxy groups, for example, phenyl    or naphthyl, and aralkyl containing from 6 to 10 carbons in the aryl    moiety and from 1 to 6 carbon atoms in the alkyl moiety, for    example, benzyl,-   B denotes C₆-C₁₀ arylene, such as 1,2-, 1,3- and 1,4-phenylene,    1,2-, 1,3-, 1,4-, 1,5- and 2,6-naphthylene, optionally substituted    by 1, 2, or 3 halogens, C₁-C₆ alkyls, esters, or alkoxy groups and-   D denotes —NH₂, —NHR³, OH, SH, or a structural element    —X—R²(—Y)_(π), the variants having the meanings stated above for    formula (I).

The acetophenone or benzophenone derivatives conforming to the generalformula (VI) can, for example, be [2, 3, or 4]-hydroxyacetophenone, [2,3 or 4]-hydroxypropiophenone, [2, 3, or4]-(2-hydroxyethoxy)acetophenone, [2, 3, or 4]-aminoacetophenone, [2-, 3or 4]-aminopropiophenone, and [2, 3, or 4]-hydroxybenzophenone,2-hydroxy-5-methylbenzophenone, 5-chloro-2-hydroxybenzophenone,2-hydroxy-4-methylbenzophenone, [2, 3, or4]-(2-hydroxyyethoxy)benzophenone, 4-hydroxy-4′-methoxybenzophenone, and[2, 3, or 4]-aminobenzophenone, [2, 3, or 4]-anilinobenzophenone,2-amino-4-methylbenzophenone, 2-amino-4′-methylbenzophenone,2-amino-4′-chlorobenzophenone, or 2-amino-5-chlorobenzophenone.

In particular, preference is given to [2 or 4]-hydroxyacetophenone, [2or 4]-hydroxypropiophenone, [2 or 4]-(2-hydroxyethoxy)acetophenone, [2or 4]-aminoacetophenone, [2 or 4]-aminopropiophenone, and [2 or4]-hydroxybenzophenone, [2 or 4]-(2-hydroxyethoxy)benzophenone, and [2or 4]-aminobenzophenone used.

The copolymerizable photoinitiators are usually produced by placing atleast one compound b), frequently together with an organic solvent, in areaction vessel under an atmosphere of inert gas, preferably nitrogen,where it is heated to the reaction temperature with stirring. There isthen added, continuously or batchwise, at least one compound a) at thereaction temperature. The amount of compound a) is governed by thenumber π of isocyanate-reactive groups and is usually such that theratio of the number of mols of compound b) to the product of the numberof moles of compound a) and the number π is from 0.8 to 1 to 1 to 0.8 orfrom 0.9 to 1 to 1 to 0.9 or from 0.95 to 1 to 1 to 0.95. If compound a)has, for example, only one isocyanate-reactive group Y (π=1), there areused, per mol of compound b), ≧0.8 mol, ≧0.9 mol, or ≧0.95 mol and ≦1.05mol, ≦1.11 mol, or ≦1.25 mol of compound a). If however, compound a)possesses, for example, two isocyanate-reactive groups Y (π=2), therewill be used, per mol of compound b), ≧0.4 mol, ≧0.45 mol, or ≧0.48 moland ≦0.53 mol, ≦0.56 mol, or ≦0.63 mol of compound a).

The reaction time is usually such that compound a) reacts quantitativelywith compound b). Usually therefore the content of isocyanate groups inthe reaction mixture is monitored during the reaction of compound a)with compound b), which content remains constant when compound a) hasreacted. Determination of the content of isocyanate groups is familiarto the person skilled in the art and is usually carried out by adding anexcess of amine, based on the isocyanate groups, and back titrating theamino groups not consumed with dilute hydrochloric acid as specified inDIN 53,185.

The aforementioned reaction is particularly successful when carried outin the presence of a catalyst, which is used in a concentration of from0.0001 to 1 wt % and preferably from 0.001 to 0.1 wt %, based on theweight of isocyanate compound b). Suitable catalysts are organometalliccompounds, specifically organotin, organozinc, organobismuth, ororganozirconium compounds. Particularly preferred is dibutyltindilaurate. Strong bases, preferably nitrogen-containing compounds, suchas tributylamine, quinnuclidine, diazabicyclooctane, diazabicyclononane,or diazabicycloundecane may also be used.

Suitable solvents are anhydrous organic solvents, such as acetone,2-butanone, ethyl acetate, butyl acetate, tetrahydrofuran, dioxan,benzene, toluene, xylene, ethylbenzene, chlorobenzene, dichlorobenzene,dimethylformamide, dimethyl acetamide, or N-methylpyrrolidone. Inparticular, acetone, 2-butanone, tetrahydrofuran, ethyl acetate, orchlorobenzene are used.

The reaction temperature is usually from 0° to 120° C., preferably from200 to 100° C., and more preferably from 25° to 90° C. The reaction maybe carried out under ambient pressure or under superatmosphericpressure, for example, under a pressure of ≧0.1 bar, ≧0.5 bar, ≧2 bar,or ≧25 bar. Of course, the reaction may be carried out undersubatmospheric pressure, depending on the boiling point of the solvent,if used.

In a subsequent second reaction stage, the reaction mixture emergingfrom the aforementioned reaction of compounds a) and b) is admixed withcompound c) continuously or batchwise at the reaction temperature. Theamount of compound c) used is governed by its number ofisocyanate-reactive groups and the number of isocyanate groups stillfree in compound b). It is usually such that the isocyanate groups incompound b) are converted quantitatively and can no longer be detectedtitrimetrically as specified in DIN 53,185. This is usually the casewhen the isocyanate content of the reaction mixture is ≦0.1 wt % ofisocyanate groups, which corresponds to the detection limit oftitration.

Another possibility, of course, is to cause compound b) to react firstof all with compound c) and then with compound a) or to cause compoundb) to react concurrently with compound a) and compound c). However, itis important that the reactions are controlled such that after theaddition of compounds a) and c) to the reaction mixture no moreisocyanate can be detected. Preferably however, compound b) is caused toreact first with compound a) and then with compound c).

The resulting reaction mixtures contain, as products, copolymerizablephotoinitiators of the general formula (VII)[H₂C═CR¹—C(═O)—X—R²(—Y′—C(═O)—NH_(π)]_(φ)-Q-[NH—C(═O)-D′-B—C(═O)A]_((λ-Ψ))  (VII),in which R¹, X, and R², π, Q, λ, B and A have the meanings given forformulas (I), (V) and (VI) and

-   φ stands for a number Ψ≧0.8, ≧0.9 or ≧0.95 and ≦1.05, ≦1.11 or ≦1.25    in each case divided by the value of π,-   Y′ stands for a group Y in the deprotonated form (—O—, —NH—, —NR³—,    —S—) and-   D′ stands for a group D in the deprotonated form [—O—, —NH—, —NR³—,    —S— and —XR²(—Y′)_(π)].

In particular, each of π, Ψ and φ denotes a numerical value of 1.

Preferably the copolymerizable photoinitiators used are compoundsconforming to formula (VII), in which

R¹ denotes —H, X and Y′ denote —O—, R² denotes ethylene, Q denotes2,4-toluenyl, D′ denotes —O—CH₂CH₂—O—, B denotes 1,4-phenylene and Adenotes phenyl, π and Ψ denote 1 and λ denotes 2, or

R¹ denotes —H, X and Y′ denote —O—, R² denotes ethylene, Q denotes3-methylene-3,5,5-trimethyl-1-cyclohexyl, D′ denotes —O—CH₂CH₂—O—, Bdenotes 1,4-phenylene and A denotes phenyl, π and Ψ denote 1 and λdenotes 2, or

R¹ denotes —H, X and Y′ denote —O—, R² denotes ethylene, Q denotes1,6-hexamethylene, D′ denotes —O—CH₂CH₂—O—, B denotes 1,4-phenylene andA denotes phenyl, π and Ψ denote 1 and λ denotes 2.

Usually the copolymerizable photoinitiators of the invention are usedfor copolymerization in the reaction mixture without furtherpurification or removal of solvent.

The copolymers of the invention are obtained by polymerization of amixture of ethylenically unsaturated monomers, in which thephotoinitiators of the invention are usually present in a total amountof from 0.01 to 10 wt %, preferably from 0.05 to 5 wt % and morepreferably from 0.1 to 2 wt %, based, in each case, on the total amountof monomers. Correspondingly, the photoinitiators of the invention areincorporated as polymerized units in the copolymers in concentrations offrom 0.01 to 10 wt %, preferably from 0.05 to 5 wt %, and morepreferably from 0.1 to 2 wt %. It should be noted here that the saidpercentage contents of the polymerized units of ethylenicallyunsaturated copolymerizable photoinitiators incorporated in thecopolymer plus the contents of the other monomers should generallycorrespond to the concentrations of these components in the monomermixture to be polymerized and vice versa.

The copolymers contain, besides the aforementioned photoinitiators,polymerized units of the main monomers generally in major amounts,comprising in most cases from 50 to 99.99 wt % and preferably from 70 to97.5 wt % of esters of preferably C₃₋₆ α,β-monoethylenically unsaturatedmono- and di-carboxylic acids, such as, in particular, acrylic acid,methacrylic acid, maleic acid, fumaric acid, and itaconic acid, withgenerally C₁-C₁₂, preferably C₁₋₈ and more preferably C₁₋₄ alkanols,such as, in particular, methyl, ethyl, n-butyl, isobutyl, and2-ethylhexyl(meth)acrylates, dimethyl maleate or di-n-butyl maleate.Suitable comonomers are, in particular, monomers that are capable ofundergoing simple free-radical polymerization, such as ethylene,vinylaromatic monomers, such as styrene, α-methylstyrene,o-chlorostyrene or vinyl toluenes, esters of vinyl alcohol and C₁₋₁₈monocarboxylic acids, such as vinyl acetate, vinyl propionate,vinyl-n-butyrate, vinyl laurate and vinyl stearate, nitriles ofα,β-monoethylenically unsaturated carboxylic acids, such asacrylonitrile, and C₄-C₈ conjugated dienes, such as 1,3-butadiene andisoprene.

It is particularly advantageous when the copolymers contain, in additionto the aforementioned monomers, from 0.1 to 15 wt %, and preferably from0.5 to 8 wt % of C₃₋₆ α,β-monoethylenically unsaturated mono- anddi-carboxylic acids, amides thereof, and/or anhydrides thereof, such as,in particular, acrylic acid, methacrylic acid, maleic acid, fumaricacid, itaconic acid, acrylamide, methacrylamide, maleic anhydride, alsovinylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid,styrenesulfonic acid and their water-soluble salts, andN-vinylpyrrolidone.

The copolymers can contain, in addition to the above monomers, furthercomonomers incorporated as polymerized units, for example, those whichusually increase the structural strength of films produced from thecopolymers. These ethylenically unsaturated monomers normally exhibit atleast one epoxy, hydroxyl, N-methylol or carbonyl group, or at least twonon-conjugated ethylenically unsaturated double bonds. Examples thereofare N-alkylolamides of α,β-monoethylenically unsaturated carboxylicacids having from 3 to 10 carbon atoms, of which N-methylol acrylamideand N-methylol methacrylamide are very much preferred, and also theiresters with alkanols containing from 1 to 4 carbons. Also suitable aremonomers having two alkenyl radicals, monomers having two vinylidenegroups and monomers having two vinyl groups. Particularly advantageoushere are the diesters of dihydroxylic alcohols withα,β-monoethylenically unsaturated monocarboxylic acids, of which acrylicacid and methacrylic acid are particularly preferred. Examples of suchmonomers containing two non-conjugated ethylenically unsaturated doublebonds are alkylene glycol diacrylates and dimethacrylates such asethylene glycol diacrylate, 1,2-propylene glycol diacrylate,1,3-propylene glycol diacrylate, 1,3-butylene glycol diacrylate,1,4-butylene glycol diacrylates and ethylene glycol dimethacrylate,1,2-propylene glycol dimethacrylate, 1,3-propylene glycoldimethacrylate, 1,3-butylene glycol dimethacrylate, 1,4-butylene glycoldimethacrylates, and divinyl benzene, vinyl methacrylate, vinylacrylate, allyl methacrylate, allyl acrylate, diallyl maleate, diallylfumarate, methylene bisacrylamide, cyclopentadienyl acrylate, triallylcyanurate, or triallylisocyanurate. Particularly significant in thiscontext are in addition C₁-C₈-hydroxyalkyl (meth)acrylates such asn-hydroxyethyl, n-hydroxypropyl or n-hydroxybutyl (meth)acrylates, andcompounds such as diacetoneacrylamide andacetylacetoxyethyl(meth)acrylate. In the present invention, theaforementioned monomers are frequently incorporated as polymerized unitsin amounts of from 0.1 to 10 wt %, based on the total weight of themonomers to be polymerized.

The manner in which the monomeric components are to be added to thepolymerization vessel during the free-radical polymerization, is knownto the person possessing average skill in the art. These can be placedin the polymerization vessel as a single initial batch, or they can beadded continuously or batchwise at the rate at which they are consumedduring the free-radical polymerization. Specifically, this depends onthe chemical nature of the initiator system and on the polymerizationtemperature. Preferably a small portion of the monomeric components isused as initial batch and the rest is fed to the polymerization zone atthe rate at which it is consumed. Another possibility, of course, is tomodify the composition of the monomer mixture to be polymerized, duringpolymerization. These process variants are known to the person skilledin the art. For example, in the so-called step method first of all amonomer mixture 1 and then a monomer mixture 2 having a differentmonomeric composition will be fed to the polymerization vessel at therate at which the monomers are consumed, whilst in the so-calledgradient method the composition of the monomer mixture that is fed tothe polymerization vessel will be continuously changed. Frequently thepolymerization is carried out under an atmosphere of inert gas, forexample, under a blanket of nitrogen or argon.

The copolymers of the invention usually have K values of from 10 to 150and often of from 15 to 100. Determination of the K value is carriedout, usually at 25° C. according to DIN ISO 1628-1, on a 1 wt % strengthsolution of the copolymer in tetrahydrofuran. Preferably the K value isfrom 25 to 55 when the copolymer is to be used as a hot-melt adhesive.When the copolymer is to be used in a UV-curable composition for coatingmineral surfaces, its K value is preferably from 60 to 100. Copolymersdesigned for use in coating compositions preferably have K values offrom 15 to 85.

The copolymers of the invention can exhibit glass transitiontemperatures of from −70 to +150° C. Depending on the end use,copolymers are frequently required whose glass transition temperaturesare within certain limits. By suitably selecting the ethylenicallyunsaturated monomers to be polymerized, the person skilled in the artcan produce copolymers whose glass transition temperatures aredefinitely in the desired range. If, for example, the copolymers of theinvention are to be used as contact-bonding adhesives, the compositionof the monomer mixture to be polymerized is such that the copolymersproduced have glass transition temperatures of <0° C., frequently ≦+5°C., and often ≦+10° C. If, however, the copolymers are to be used asUV-curable binding agents in coating compositions, the composition ofthe monomer mixture to be polymerized is such that the copolymersproduced show glass transition temperatures of from −40° to +150° C.,frequently from 0° to +100° C., and often from +20° to +80° C.

By the glass transition temperature T_(g), we mean the limiting value ofthe glass transition temperature which it approaches with increasingmolecular weight as described by G. Kanig (Kolloid-zeitschrift &Zeitschrift fr Polymere, Vol. 190, page 1, equation 1). The glasstransition temperature is determined by the DSC method (DifferentialScanning Calorimetry, 20 K/min, mid-point reading, DIN 53,765).

According to Fox (T. G. Fox, Bull. Am. Phys. Soc. 1956 [Ser. II] 1, page123 and according to Ullmanns Encyclopaedie der technischen Chemie, Vol.19, page 18, 4th Edition, Verlag Chemie, Weinheim, 1980) the followingapplies to the glass transition temperature of not more than weaklycrosslinked copolymers, as a good approximation:1/T _(g) =x ¹ /T _(g) ¹ +x ² /T _(g) ² + . . . x _(n) /T _(g) ^(n),in which x¹, x² . . . x^(n) denote the mass fractions of the monomers 1,2 . . . n and T_(g) ¹, T_(g) ² . . . T_(g) ^(n) denote the glasstransition temperatures of the polymers composed of, in each case, onlyone of the monomers 1, 2 . . . n, in degrees Kelvin. The T_(g) valuesfor the homopolymers of most monomers are known and are listed, forexample, in Ullmann's Encyclopedia of Industrial Chemistry, Vol. 5, Vol.A21, page 169, VCH Weinheim, 1992; further sources of glass transitiontemperatures of homopolymers are, eg, J. Brandrup, E. H. Immergut,Polymer Handbook, 1^(st) Ed., J. Wiley, New York 1966, 2^(nd) Ed. J.Wiley, New York 1975, and 3rd Ed. J. Wiley, New York 1989).

The novel copolymers can be produced by copolymerization of themonomeric components using conventional polymerization initiators and,optionally, modifiers, polymerization being carried out at the usualtemperatures in substance, in emulsion, for example, in water orsuitable organic media, or in solution. Preferably, the novel copolymersare produced by polymerization of the monomeric components in organicsolvents, particularly in solvents having a boiling range of from 50° to150° C., preferably from 60° to 120° C., using conventional amounts ofpolymerization initiators, which are generally from 0.01 to 10 wt %, andparticularly from 0.1 to 4 wt %, based, in each case, on the totalweight of the monomeric components. Suitable organic solvents are, inparticular, alcohols, such as methanol, ethanol, n-propanol,isopropanol, n-butanol and isobutanol, cyclic ethers, such astetrahydrofuran, and hydrocarbons, such as toluene and gasolenes boilingat temperatures ranging from 60° to 120° C. Furthermore ketones, such asacetone, methyl ethyl ketone and esters, such as ethyl acetate, andmixtures of solvents of said types can be used, in which case mixturescontaining isobutanol and/or methyl ethyl ketone in amounts of ≧70 wt %,particularly ≧80 wt %, and more particularly ≧90 wt %, based on thesolvent mixture used are preferred.

The manner in which the solvent or solvent mixture is added to thepolymerization vessel during the free-radical polymerization, is knownto the person possessing average skill in the art. It can be placed as asingle initial batch in the polymerization vessel, or it can be usedcontinuously or stepwise during the free-radical polymerization. Inaddition, the solvent can be used in admixture with the monomers and/orthe initiator. Preferably, a major portion of the solvent is used asinitial batch and the rest is fed to the polymerization zone togetherwith the monomers to be polymerized and/or initiators.

Suitable polymerization initiators for solvent polymerization are, forexample, azo compounds, such as 2,2′-azobisisobutyronitriue,2,2′-azobis-2-methylbutyronitrile, diacyl peroxides, such as dibenzoylperoxide, dilauroyl peroxide, didecanoyl peroxide, and diisononanoylperoxide, alkyl peresters, such as tert-butyl perpivalate, tert-butylper-2-ethylhexanoate, tert-butyl permaleate, tert-butyl perisononanoate,and tert-butyl perbenzoate, dialkylperoxides, such as dicumyl peroxideor di-tert-butyl peroxide, peroxydicarbonates, such as dimyristylperoxydicarbonate, dicetyl peroxydicarbonate,bis(4-tert-butylcyclohexyl) peroxydicarbonate, dicyclohexylperoxydicarbonate, bis(2-ethylhexyl) peroxydicarbonate, andhydroperoxides, such as tert-butyl hydroperoxide, and cumenehydroperoxide, alone or intermixed. In aqueous emulsion polymerization,conventional initiators, such as sodium, potassium, and ammoniumperoxodisulfates or alternatively redox systems known to the personskilled in the art can be used.

The manner in which the initiator is added to the polymerization vesselduring the free-radical polymerization, is known to the personpossessing average skill in the art. It may be placed in thepolymerization vessel as a single initial batch, or it may be usedcontinuously or stepwise at the rate at which it is consumed during thefree-radical polymerization. Specifically, this depends on the chemicalnature of the initiator system and on the polymerization temperature.Preferably, a small portion is used as initial batch and the rest is fedto the polymerization zone at the rate at which it is consumed. It isfrequently advantageously when the polymerization reaction is controlledsuch that first of all ≦50 wt %, often ≦45 wt %, or ≦40 wt % of theinitiator is fed to the polymerization vessel continuously over arelatively long period of time and then >50 wt %, often ≧55 wt %, or ≧60wt % of the initiator is fed in continuously over a shorter period oftime.

Polymerization can be carried out in conventional manner inpolymerization apparatus, generally equipped with an agitator, severalfeed boxes or feed pipes, a reflux condenser and heating and coolingmeans and designed for operation under an atmosphere of inert gas underpressures above or below atmospheric pressure.

Following polymerization in solution, the solvents can be separated,optionally under reduced pressure, this being done at an elevatedtemperature of up to 150° C. The novel copolymers can then be used in alow-solvent or solventless state, ie as a melt, as adhesives, preferablyself-adhesives and, in particular, hot-melt adhesives, or as UV-curablebinding agents in coating compositions, such as protective materials forcoating mineral surfaces or as paints. It may in many cases beadvantageous to prepare the novel copolymers by copolymerization insubstance, ie without the assistance of a solvent, in which caseproduction may take place batchwise or continuously, for example, asdescribed in U.S. Pat. No. 4,042,768.

If the novel copolymers are used in the form of solutions, for example,as UV-curable binding agents in coating compositions, such as protectivematerials for coating mineral surfaces or as paints, the copolymersolutions usually contain from 1 to 900 parts by weight, preferably from10 to 100 parts by weight, and more preferably from 20 to 40 parts byweight of solvent per 100 parts by weight of copolymer. Frequently, thecopolymer solutions obtained by solvent polymerization can be usedunchanged for these purposes, or they can be produced therefrom bysimple dilution or concentration.

In some cases, for example, when the novel copolymers are produced byaqueous free-radical emulsion polymerization, it is possible to includeconventional regulators in conventional amounts, for example, inconcentrations of from 0.1 to 10 parts by weight or from 0.5 to 5 partsby weight per 100 parts by weight of the monomers to be polymerized.Such regulators are used for the regulation of the molecular weight ofthe copolymers and are known to the person skilled in the art.Frequently, use is made of mercapto compounds, such as2-mercaptoethanol, methyl 3-mercaptopropionate,3-mercaptopropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane,3-mercaptopropionic acid, n- or tert-dodecyl mercaptan,1,6-dimercaptohexane, 1,9-dimercaptononane, hydrocarbons, such ascumene, alcohols, such as isopropanol and isobutanol or halogenatedhydrocarbons, such as carbon tetrachloride, carbon tetrabromide,chloroform, or bromoform, ethers, such as tetrahydrofuran and dioxan, asregulators.

If the novel copolymers are produced by aqueous free-radical emulsionpolymerization, polymerization is usually carried out in the presence ofdispersing agents. The dispersing agents used can be protective colloidsand/or emulsifiers as are familiar to the person skilled in the art, forexample, non-ionic and anionic or cationic emulsifiers. Preferably,non-ionic and anionic emulsifiers are used. The concentration ofdispersant is usually up to 30 parts by weight, preferably from 0.5 to10 parts by weight, and more preferably from 1 to 6 parts by weight,based on 100 parts by weight of the monomers to be polymerized.

Frequently, unconverted monomers are removed from the reaction mixtureon completion of copolymerization. In the case of solventpolymerization, this is carried out at the same time as the removal ofsolvent under reduced pressure. In order to increase the efficiency,particularly on an industrial scale, the copolymer is stripped withsteam when the solvent has been removed. This steam stripping islikewise frequently carried out on completion of free-radical emulsionpolymerization, optionally after an interposed post-polymerization step,such as is known to the person skilled in the art, for example, fromspecifications WO 95/33775, EP-A 767,180, or DE-A 19743759. It issignificant that the photoinitiators of the invention, in copolymerizedor non-copolymerized form, show better resistance to hydrolysis by wateror other protic organic solvents, such as isopropanol or isobutanol,than the copolymerizable photoinitiators of the prior art.

When use is made of the novel copolymers, they can be modified inconventional manner and/or subjected to ancillary processing and, forexample, used as hot-melt adhesives. Thus there can be added, forexample, conventional tackifying resins, for example, hydrocarbonresins, modified natural colophoniums or chemically modifiedcolophoniums, predominantly consisting of abietic acid or abietic acidderivatives, coumaron-indene resins, terpenephenolic resins, aldehyderesins, or homopolymers, such as poly-2-ethylhexyl acrylate orpoly-α-methylstyrene, further plasticizers, for example, those based onmono-, di- or poly-ester compounds, perchlorinated hydrocarbons orparaffin oils, dyes, and pigments or stabilizing agents orrubber-elastic materials, such as natural or synthetic rubbers,polyvinyl ethers, and also polybutadiene oils, in amounts of from 0.1 to50 wt %, based on the total weight.

Also suitable for modification are mono- or poly-olefinicallyunsaturated polymolecular compounds, such as polyesterols andpolyetherols esterified with acrylic acid, such as the acrylates oftripropylene glycol, tetraethylene glycol, or other polyethylhncglycols. Likewise suitable are diacrylates and dimethacrylates ofpolytetrahydrofuran having molecular weights of, in most cases, from 250to 2000 (number average). Such diolefinically or polyolefinicallyunsaturated compounds may be advantageously used in concentrations offrom 0.1 to 10 parts by weight per 100 parts by weight of copolymer, anddiolefinically unsaturated compounds of this kind having a molecularweight of at least 500 (number average) are of particular interest.

The novel copolymers are particularly suitable for use as melts orsolutions or in the form of aqueous dispersions for the production ofcoatings, protective films and impregnations, and particularlypressure-sensitive adhesives, self-adhesive films, self-adhesive labels,and embossed films. The compositions can be applied in conventionalmanner by brush coating, spraying, rolling, knife coating or pouring,optionally at elevated temperature—mostly in the temperature range offrom 20° to 150° C.—on conventional substrates, for example, paper,paperboard, wood, metals, such as aluminum, plastics films, such asflexible PVC, polyethylene, polyamides, polyethylene glycolterephthalate, and polypropylene.

If solvents are used, they can be readily evaporated off from thecoatings, optionally at room temperature or slightly elevatedtemperatures, generally at temperatures of from 20° to 150° C. andpreferably at from 50° to 80° C., for which purpose radiant heaters orhot-air rotary blowers are usually used. The possibly dried or predriedcoatings can then be UV-crosslinked by irradiation to give highlyadhesive coatings exhibiting high cohesion combined with good adhesionand excellent resistance to ageing. Irradiation with UV light normallyrequires no inert gas conditions and can usually take place in air. TheUV radiators used can be conventional radiators, for example, low-,medium-, and high-pressure mercury arc lamps having a power output offrom 20 to 100 J/sec×cm². Lamps of higher power output generally causefaster crosslinking. In some cases, the crosslinking irradiation may beaccompanied, due to the infra-red emission of the lamps, by the removalof residual solvent or water.

The adhesive properties of flat substrates exhibiting a self-adhesivelayer can be determined by measuring the shear strength as a measure ofcohesion and the peel strength as a measure of surface tack.

EXAMPLES I Production of Copolymerizable Photoinitiators I a) Ethyleneglycol p-benzophenone ether

In a laboratory autoclave having a capacity of 2 L there were placed 520g of diethylene glycol diethyl ether, 286 g of p-hydroxybenzophenone(>98 wt %), and 0.8 g of powdered potassium hydroxide. A pressure testwas then carried out for 30 minutes using dry nitrogen. Followingpressure let-down to atmospheric pressure and heating of the reactionmixture under a blanket of nitrogen to 120° C., 95.4 g of ethylene oxidewere continuously forced in to give a maximum internal pressure of 4 barover a period of 1 h. On completion of gassing with ethylene oxide, thereaction mixture was allowed to react, until the pressure remainedconstant for at least 30 minutes. The reaction mixture was dischargedfrom the autoclave in the hot state, neutralized with 5 wt % strengthaqueous hydrochloric acid, and poured into 2 L of ice water, and thereaction product was caused to crystallize by constant agitation. Theresulting solid matter was filtered off in vacuo, washed with ice waterand dried in vacuo (40° C., 10 mbar absolute). The resulting filtratewas concentrated in a rotary film evaporator to 20% of its volume, theprecipitated product filtered off in vacuo, washed with ice water andlikewise dried in vacuo. The total yield was 82% of theory.

I b) Copolymerizable Photoinitiators, General Production Instructions

1 mol of isocyanate as given in Table 1 was dissolved in anhydroustetrahydrofuran (THF) at from 20° to 25° C. (ambient temperature) suchthat the urethane adduct produced in the first reaction stepsubsequently existed as a 35 wt % strength solution. After covering withdry nitrogen, 1 mol of hydroxyethyl acrylate, previously stabilized with100 ppm of Tempol, was then added within a period of 5 minutes at roomtemperature. 500 ppm by weight (based on isocyanate used) of dibutyltindilaurate were then added, and the mixture was stirred for approximately5 hours at 50° C. while the fall in isocyanate content was monitoredtitrimetrically. Once the theoretical isocyanate content of themonourethane had been achieved, the molar amount of ethylene glycolp-benzophenone ether groups corresponding to the isocyanate still freeis added as a 35 wt % strength solution from stage Ia) in THF having atemperature of 50° C. The reaction mixture was then further stirred at50° C. until no more isocyanate groups could be detectedtitrimetrically. The resulting reaction mixtures were used directly inthe following polymerization reaction.

TABLE 1 Isocyanates and solvents Photoinitiator Isocyanate A2,4-toluylene diisocyanate B isophorone diisocyanate CHDI-polyisocyanate 2,4-Toluylene diisocyanate: 95 wt %, Fluka AGisophorone diisocyanate: Vestanat ®IPDI, Degussa-Hls AGHDI-polyisocyanate: Basonat ® HI 100, BASF AG dibutyltin dilaurate: 95wt %, Merck-Schuchardt tetrahydrofuran: 99.9 wt %, anhydrous2-hydroxyethyl acrylate: >98.5 wt %, BASF AG Tempol: 2,2,6,6-tetramethylpiperidin-1-oxyl-4-ol, 98 wt %, Aldrich-Chemie

I c) 4-(4-benzoylphenoxycarbonyloxy)-n-butyl acrylate (comparativephotoinitiator)

The synthesis of 4-(4-benzoylphenoxycarbonyloxy)-n-butyl acrylate wascarried out according to the teaching of EP-A 377,199. In thecomparative example, a 35 wt % strength solution of the comparativephotoinitiator in o-xylene was used.

II Production of the Copolymers Example 1

In a reactor having a capacity of 2 L and provided with heating andcooling means and equipped with an anchor agitator, reflux condenser andevacuating and metering equipment there were placed, at room temperatureunder a blanket of nitrogen,

-   108.5 g of isobutanol (IB; 99.5 wt %)-   50.5 g of feed stream 1 and-   4.3 g of feed stream 2    and the mixture was heated to 100° C. with stirring with the    apparatus closed but without pressure compensation. Starting    concurrently, the residual amount of feed stream 1 was metered in at    this temperature over a period of 3 hours and the residual amount of    feed stream 2 over a period of 3.5 hours. 15 minutes after    completion of feed 2, feed 3 was commenced, this being metered in    over a period of 15 minutes. At the same time as feed stream 3 was    metered, the temperature was raised to 120° C.

On conclusion of feed 3, polymerization was continued for a further hourat 120° C. The temperature was then lowered to 100° C. and the pressuregently let down to atmospheric pressure, after which the solvent and theother low-boiling components were removed by distillation by carefulapplication of vacuum to a final pressure of 10 mbar (absolute). Thereaction batch was then cooled to room temperature.

Feed Stream 1

-   491.0 g of n-butyl acrylate (n-BA; ≧99.5 wt %, BASF AG)-   278.5 g of 2-ethylhexyl acrylate (EHA; ≧99.6 wt %, BASF AG)-   189.0 g of methyl methacrylate (MMA; ≧99.9 wt %, BASF AG)-   23.0 g of acrylic acid (AA; ≧99.0 wt %, BASF AG)-   15.1 g of a 35 wt % strength solution of photoinitiator A in THF    Feed Stream 2-   41.7 g of IB-   0.3 g tert.-Butylper-2-ethylhexanoat (TBEH; ≧-   98.5 wt %, sold by Peroxid-Chemie GmbH)    Feed Stream 3-   16.7 g of IB-   2.0 g of TBEH

There was obtained a clear, highly viscous polymer having a solidscontent of >99.9 wt %.

The solids content was generally determined by heating from 1 to 2 g ofthe resulting polymer at 140° C. to constant weight in an aluminumcrucible having a diameter of ca 3 cm, under atmospheric pressure. Ineach case two readings were taken. The values given represent theaverages of these readings. In all of the following examples solidscontents of ≧99.9 wt % were likewise found.

The K value of the copolymer was 50.5.

The K values of the copolymers were generally determined as specified byH. Fikentscher, Cellulosechemie 1932 (13) pages 58 to 64 and pages 71 to74, where K is equal to k×103. The readings were taken at 25° C. on a 1wt % strength solution of the copolymers in THF (corresponding to DINISO 1628-1).

COMPARATIVE EXAMPLE

The comparative example was carried out in a manner similar to thatdescribed in Example 1 with the exception that instead of 45 thephotoinitiator A the same amount of the comparative photoinitiator wasused. The K value was found to be 50.5.

Example 2

Example 2 was carried out in a manner similar to that described inExample 1 exception that instead of IB use was made of methyl ethylketone (MEK; ≧99.0 wt %, Deutsche Shell Chemie GmbH). A K value of 51.8was found.

Example 3

Example 3 was a repetition of Example 1 except that instead of thephotoinitiator A the identical amount of photoinitiator B was used. TheK value was found to be 48.0.

Example 4

Example 4 was a repetition of Example 1 except that instead of thephotoinitiator A the identical amount of photoinitiator C was used. TheK value was found to be 48.6.

Example 5

Example 5 was a repetition of Example 1 except that 30.2 g of a 35 wt %strength solution of photoinitiator A in THF were used. The K value wasfound to be 52.0.

Example 6

Example 6 was a repetition of Example 1 except that in the feed streams2 and 3 instead of TBEH 2,2′-azobis-2-methylbutyronitrile (Wako V59,WAKO Chemicals GmbH) were used. The K value was found to be 49.6.

Example 7

In a reactor having a capacity of 2 L and provided with heating andcooling means and equipped with an anchor agitator, reflux condenser andevacuating and metering equipment

-   110.5 g of IB-   52.5 g of feed stream 1 and-   4.0 g of feed stream 2    were used as initial batch at room temperature under a blanket of    nitrogen and heated to 100° C. in closed apparatus without pressure    compensation, with stirring. Starting concurrently, the residual    amount of feed stream 1 was metered in at this temperature over a    period of 3 hours and the residual amount of feed stream 2 over a    period of 3.5 hours. 15 minutes after completion of feed 2, feed 3    was commenced, this being metered in over a period of 15 minutes. At    the same time as feed stream 3 was metered, the temperature was    raised to 120° C.

On conclusion of feed 3, polymerization was continued for a further hourat 120° C. The temperature was then lowered to 100° C. and the pressurecarefully let down to atmospheric pressure, after which the solvent andother low-boiling components were removed by distillation by gentleapplication of vacuum to a final pressure of 10 mbar (absolute). Thebatch was then cooled to room temperature. There was obtained a clear,highly viscous polymer having a solids content of >99.9 wt %. The Kvalue was found to be 50.5.

Feed Stream 1

-   422.0 g of n-BA-   347.5 g of EHA-   189.0 g of MMA-   25.0 g of AA-   12.3 g of a 35 wt % strength solution of photoinitiator A in THF    Feed Stream 2-   41.7 g of IB-   0.4 g of TBEH    Feed Stream 3-   16.7 g of IB-   2.4 g of TBEH

Example 8

Example 8 was carried out in a manner similar to that described inExample 7 except that instead of IB there was used MEK. A K value of48.8 was found.

Example 9

Example 9 was a repetition of Example 7 except that instead of thephotoinitiator A the identical amount of photoinitiator B was used. TheK value was found to be 48.6.

Example 10

Example 10 was a repetition of Example 7 except that instead of thephotoinitiator A the identical amount of photoinitiator C was used. TheK value was found to be 48.6.

Example 11

Example 5 was a repetition of Example 7 except that 24.6 g of a 35 wt %strength solution of photoinitiator A in THF were used. The K value wasfound to be 50.2.

Example 12

Example 12 was a repetition of Example 7 except that in the feed streams2 and 3 instead of TBEH Wako V59 was used. The K value was found to be48.5.

Example 13

In a reactor having a capacity of 2 L and provided with heating andcooling means and equipped with an anchor agitator, reflux condenser andevacuating and metering equipment

-   115.0 g of IB-   59.5 g of feed stream 1 and-   3.3 g of feed stream 2    were used as initial batch at room temperature under a blanket of    nitrogen and heated to 100° C. in closed apparatus without pressure    compensation, with stirring. Starting concurrently, the residual    amount of feed stream 1 was metered in at this temperature over a    period of 3.5 hours and the residual amount of feed stream 2 over a    period of 4 hours. 15 minutes after completion of feed 2, feed 3 was    commenced, this being metered in over a period of 15 minutes. At the    same time as feed stream 3 was metered, the temperature was raised    to 115° C.

On conclusion of feed 3, polymerization was continued for another twohours at 115° C. The temperature was then lowered to 100° C. and thepressure carefully let down to atmospheric pressure, after which thesolvent and other low-boiling components were removed by distillation bygentle application of vacuum to a final pressure of 10 mbar (absolute).The batch was then cooled to room temperature. There was obtained aclear, highly viscous polymer having a solids content of >99.9 wt %. TheK value was found to be 50.1.

Feed Stream 1

-   1117.0 g of n-BA-   59.1 g of AA-   11.5 g of a 35 wt % strength solution of photoinitiator A in THF    Feed Stream 2-   65.8 g of IB-   1.3 g of TBEH    Feed Stream 3-   19.7 g of IB-   2.6 g of TBEH

Example 14

In a reactor having a capacity of 2 L and provided with heating andcooling means and equipped with an anchor agitator, reflux condenser andevacuating and metering equipment

-   115.0 g of IB-   59.5 g of feed stream 1 and-   3.3 g of feed stream 2    were used as initial batch at room temperature under a blanket of    nitrogen and heated to 100° C. in closed apparatus without pressure    compensation, with stirring. Starting concurrently, the residual    amount of feed stream 1 was metered in at this temperature over a    period of 3.5 hours and the residual amount of feed stream 2 over a    period of 4 hours. 15 minutes after completion of feed 2, feed 3 was    commenced, this being metered in over a period of 15 minutes. At the    same time as feed stream 3 was metered, the temperature was raised    to 115° C.

On conclusion of feed 3, polymerization was continued for another twohours at 115° C. The temperature was then lowered to 100° C. and thepressure carefully let down to atmospheric pressure, after which thesolvent and other low-boiling components were removed by distillation bygentle application of vacuum to a final pressure of 10 mbar (absolute).The batch was then cooled to room temperature. There was obtained aclear, highly viscous polymer having a solids content of >99.9 wt %. TheK value was found to be 50.5.

Feed Stream 1

-   1100.0 g of n-BA-   55.1 g of AA-   22.0 g of maleic anhydride (MA; >99.7 wt %, Lonza S.P.A.)-   11.5 g of a 35 wt % strength solution of photoinitiator A in THF    Feed Stream 2-   65.8 g of IB-   1.3 g of TBEH    Feed Stream 3-   19.7 g of IB-   2.6 g of TBEH

Example 15

In a reactor having a capacity of 2 L and provided with heating andcooling means and equipped with an anchor agitator, reflux condenser andevacuating and metering equipment

-   115.0 g of IB-   59.5 g of feed stream 1 and-   3.3 g of feed stream 2    were used as initial batch at room temperature under a blanket of    nitrogen and heated to 100° C. in closed apparatus without pressure    compensation, with stirring. Starting concurrently, the residual    amount of feed stream 1 was metered in at this temperature over a    period of 3.5 hours and the residual amount of feed stream 2 over a    period of 4 hours. 15 minutes after completion of feed 2, feed 3 was    commenced, this being metered in over a period of 15 minutes. At the    same time as feed stream 3 was metered, the temperature was raised    to 115° C.

On conclusion of feed 3, polymerization was continued for another twohours at 115° C. The temperature was then lowered to 100° C. and thepressure carefully let down to atmospheric pressure, after which thesolvent and other low-boiling components were removed by distillation bygentle application of vacuum to a final pressure of 10 mbar (absolute).The batch was then cooled to room temperature. There was obtained aclear, highly viscous polymer having a solids content of >99.9 wt %. TheK value was found to be 49.3.

Feed Stream 1

-   1043.0 g of n-BA-   133.1 g of AA-   22.0 g of a 35 wt % strength solution of photoinitiator A in THF    Feed Stream 2-   65.0 g of IB-   1.7 g of TBEH    Feed Stream 3-   19.9 g of IB-   2.6 g of TBEH

Example 16

Example 16 was carried out in a manner similar to that described inExample 15 except that the following feed streams were used:

Feed Stream 1

-   1000.0 g of n-BA-   105.1 g of AA-   72.0 g of MA-   13.5 g of a 35 wt % strength solution of photoinitiator A in THF    Feed Stream 2-   68.4 g of IB-   1.7 g of TBEH    Feed Stream 3-   19.7 g of IB-   2.8 g of TBEH

The K value was found to be 48.6.

Example 17

In a reactor having a capacity of 2 L and provided with heating andcooling means and equipped with an anchor agitator, reflux condenser andevacuating and metering equipment

-   110.0 g of IB-   59.0 g of feed stream 1 and-   2.5 g of feed stream 2    were used as initial batch at room temperature under a blanket of    nitrogen and heated to 100° C. in closed apparatus without pressure    compensation, with stirring. Starting concurrently, the residual    amount of feed stream 1 was metered in at this temperature over a    period of 4 hours and the residual amount of feed stream 2 over a    period of 4.5 hours. 15 minutes after completion of feed 2, feed 3    was commenced, this being metered in over a period of 15 minutes. At    the same time as feed stream 3 was metered, the temperature was    raised to 115° C.

On conclusion of feed 3, polymerization was continued for another twohours at 115° C. The temperature was then lowered to 100° C. and thepressure carefully let down to atmospheric pressure, after which thesolvent and other low-boiling components were removed by distillation bygentle application of vacuum to a final pressure of 10 mbar (absolute).The batch was then cooled to room temperature. There was obtained aclear, highly viscous polymer having a solids content of ≧99.9 wt %. TheK value was found to be 46.5.

Feed Stream 1

-   910.0 g of EHA-   91.0 g of hydroxyethyl acrylate (≧98.5 Gew.-%, BASF AG)-   22.2 g of a 35 wt % strength solution of photoinitiator A in THF    Feed Stream 2-   35.8 g of IB-   0.8 g of TBEH    Feed Stream 3-   21.7 g of IB-   2.8 g of TBEH

The K value was found to be 48.6.

III Utilitarian Tests

The copolymers produced in Examples from 1 to 17 were subjected toutilitarian tests to examine their self-adhesive properties. Theprocedure was as follows:

a) Production of Test Strips

The copolymer to be tested was examined without the addition oftackifiers. For this purpose the copolymer was thinly applied to acommercial polyester film (Hostaphan RN 36 film) on a heated spreadingbench at from 85° to 120° C. with a doctor blade and then cooled to roomtemperature. The radial screw clearance of the doctor blade was set togive a rate of copolymer application of from 19 to 21 g/m². Irradiationwas effected with a CK radiator, sold by IST-Strahlentechnik Metz GmbHand having a power output of 75 mJ/sec×cm². For this purpose the coatedfilm was laid on a travelling continuous web so that the coated filmpassed under the lamp at a distance of 10 cm and at a rate of 58 m/min.Irradiation took place in air. The films thus produced were cut up intotapes 2.5 cm wide and 25 cm long.

b) Test of Shear Strength (Similar to FINAT FTM 7)

Each strip was stuck to the marginal region of a test plate ofhigh-grade steel such that a stick-on area of 12.5×12.5 mm² wasobtained. 10 minutes after the strip had been stuck to the plate a 1000g weight was fixed to the loose end of the strip and the test plate washung vertically in a chamber having a constant temperature of 23° C. anda relative humidity of 50%. The time taken for the weighted tape to tearaway from the plate is a measure of the shear strength, which is in turna measure of cohesion. The more time required to break the adhesivebond, the greater the cohesion. Three separate tests were carried out oneach polymer. The values given in Table 2 are averages of the results ofsaid tests.

c) Test of the Peel Strength (Similar to FINAT FTM 1)

A test strip was stuck to a stainless steel test plate at 23° C. and 50%relative humidity.

Following a specified contact time of 24 hours, the tape was pulled offthe plate with a tension tester at an angle of 180° and at a rate of 300mm per minute. The required force is a measure of the adhesion. It istermed peel strength and is expressed in terms of newton per 2.5 cm(N/2.5 cm). The degree of adhesion is higher, the higher the value ofthe peel strength after the stated time. Three separate tests werecarried out on each polymer. The values given in Table 2 are averages ofthe results of said tests.

TABLE 2 Summary of the shear strengths and peel strengths of thecopolymers of Examples from 1 to 17 Peel strength in Shear strength inN/2.5 cm after 24 Polymer of Example minutes hours 1 135 10.2 Comparison75 9.7 2 125 12.7 3 110 17.1 4 90 17.0 5 148 10.5 6 111 12.0 7 115 12.98 105 12.1 9 108 14.3 10 101 14.0 11 137 10.9 12 106 11.1 13 130 10.5 14115 10.8 15 111 12.1 16 108 10.9 17 118 11.8

As is clearly visibly from Table 2, the hot-melt adhesives of theinvention exhibit distinctly higher shear strengths (cohesion) than aself-adhesive during the production of which a photoinitiator is usedwhich is not of the invention. Greatly improved are also the peelstrengths (adhesion) as measured after a period of 24 hours.

1. A copolymer obtainable by a process comprising free-radicallypolymerizing a mixture of ethylenically unsaturated monomers comprisinga free-radically copolymerizable acetophenone or benzophenone derivativecomprising components a), b) and c) obtained by reaction of a) a(meth)acrylic compound exhibiting at least one isocyanate-reactivegroup, compound a), with b) a compound having at least two isocyanategroups, compound b), and c) an acetophenone or benzophenone derivativeexhibiting at least one isocyanate-reactive group, compound c).
 2. Acopolymer as defined in claim 1 having a glass-transition temperature offrom −70 to +150° C.
 3. A method of binding or adhering comprisingapplying the copolymer as defined in claim 1 to a substrate.
 4. A methodof pressure-sensitively adhering a substrate comprising applying thecopolymer as defined in claim 1 to a substrate and adhering saidsubstrate to a surface.
 5. An adhesive which comprises the copolymer asclaimed in claim
 1. 6. An adhesive which comprises the copolymer asclaimed in claim
 2. 7. The copolymer of claim 1, wherein the compound a)is a (meth)acrylic compound of formula (I)H₂C═CR¹—C(═O)—X—R²(—Y)_(π)  (I), in which the substituents and indiceshave the following meanings: R¹ denotes —H, —CH₃, X denotes —O—, —NH—,—NR³— or —S—, R³ denotes linear or branched C₁-C₆ alkyl, R² denotes a(π+1)-binding, optionally substituted linear or branched C₁-C₁₂ alkylgroup, or a C₃-C₁₂ cycloalkyl group, optionally substituted, or a C₆-C₁₀aryl group, optionally substituted, Y denotes —OH, —NH₂, —NHR³, or —SH πis a number from 1 to 5, while the structural element —R²(—Y)_(π) informula (I) can alternatively be a group of formula (II), (III), or (IV)-(EO)_(k)—(PO)_(l)—H  (II),—(PO)_(l)-(EO)_(k)—H  (III),-(EO_(k)/PO_(l))—H  (IV), in which EO stands for a —CH₂—CH₂—O group, POstands for a —CH₂—CH(CH₃)—O or a —CH(CH₃)—CH₂—O group and k and l arenumerical values of from 0 to 15, but k and l are not both
 0. 8. Thecopolymer of claim 1, wherein compound b) is a compound of formula (V)Q(-NCO)_(λ)  (V), in which Q is a linear or branched C₃-C₁₆ alkanecompound, optionally substituted by 1, 2, or 3 halogens, oxo, ester, oralkoxy groups, or a C₆-C₁₄ aromatic compound, optionally substituted by1, 2, or 3 halogens, or C₁-C₆ alkyl, oxo, ester, or alkoxy groups, or aC₃-C₁₆ cycloalkane compound, optionally substituted by 1, 2, or 3halogens, C₁-C₆ alkyl, oxo, ester, or alkoxy groups, or an arylalkylcompound containing from 6 to 10 carbons in the aryl moiety and from 1to 6 carbon atoms in the alkyl moiety, optionally substituted by 1, 2,or 3 halogens, oxo, ester, or alkoxy groups, and λ is a number ≧2. 9.The copolymer of claim 1, wherein compound c) is an acetophenone orbenzophenone derivative of formula (VI)A-C(═O)—B-D  (VI), in which the substituents have the following meaning:A denotes C₁-C₃ alkyl, C₆-C₁₀ aryl, optionally substituted by 1, 2, or 3halogens, C₁-C₆ alkyl, ester, or alkoxy groups, and aralkyl containingfrom 6 to 10 carbons in the aryl moiety and from 1 to 6 carbons in thealkyl moiety, B denotes C₆-C₁₀ arylene, optionally substituted by 1, 2,or 3 halogens, C₁-C₆ alkyl, ester, or alkoxy groups and D denotes —NH₂,—NHR³, OH, SH, or a structural element —X—R²(—Y)_(λ), the variantshaving the meanings stated for formula (I).
 10. The copolymer of claim7, wherein, in compound a), Y denotes —OH and π denotes 1, in compoundb), λ denotes 2, and, in compound c), A denotes methyl or phenyl, Bdenotes 1,4-phenylene, and D denotes —O—CH₂CH₂—OH.
 11. The copolymer ofclaim 7, wherein the ratio of the number of mols of compound b) to theproduct of the number of mols of compound a) and the number π is from0.8:1 to 1:0.8.
 12. The copolymer of claim 1, wherein said acetophenoneor benzophenone derivative is present in a an amount of 0.1 to 10 wt. %based on the total amount of monomers.
 13. The copolymer of claim 1,wherein, said mixture of ethylenically unsaturated monomers comprises0.1 to 15 wt. % of C₃₋₆-monoethylenically unsaturated carboxylic acids.14. The copolymer of claim 1, wherein, said copolymer has a K value offrom 10 to
 150. 15. The copolymer of claim 2, wherein, said copolymerhas a glass transition temperature of <0° C.
 16. The copolymer of claim1, wherein, said copolymer has a glass transition temperature of 0 to100° C.
 17. The copolymer of claim 1, wherein, said copolymer has aglass transition temperature of from 20 to 80° C.